This disclosure relates generally to methods and apparatus for generating pulses in a fluid column, as may be used for telemetry between a surface location and downhole instrumentation within a subterranean well.
Drilling fluid circulated down a drill string to lubricate the drill bit and remove cuttings is typically broadly referred to as drilling “mud.” The use of pulses in a drilling fluid column is typically termed “mud pulse telemetry.” Numerous fluid pulsing systems have been used for generating such pulses in the fluid column. Such systems include various forms of valve mechanisms to produce fluid pulses. A “poppet” valve, for example, may have a valve member that linearly reciprocates, to open and close a fluid passageway. A rotary valve, by comparison, may have a rotor that rotates to selectively control flow to a fluid passageway. A rotary valve may either rotate reciprocally, to relatively open and close a fluid passage to generate pulses, or continually, wherein the speed of the rotor may be varied to facilitate pulses at a momentary selected frequency to execute a desired communication protocol. Each of these systems offers various features and characteristics.